First Resolution of a Free Fluorophosphine Chiral at Phosphorus. Resolution and Reactions of Free and Coordinated (±)-Fluorophenylisopropylphosphine

Abstract

The trivalent fluorophosphine (±)-PFPh(i-Pr), (±)-1, has been prepared by halogen exchange of the corresponding chlorophosphine with sodium fluoride in hot sulfolane. The neat fluorophosphine rapidly decomposes by quilibrium redox disproportionation into PF3Ph(i-Pr) and (R*,R*)/(R*,S*)-Ph(i-Pr)PPPh(i-Pr), but in benzene, (±)-1 has considerable thermodynamic stability. The resolution of (±)-1 was achieved by a fractional crystallization of the diastereomers (R,RP)- and (R,S P)-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N] (fluorophenylisopropylphosphine)palladium(II), (R,RP)- and (R,SP)-5, whereby the less soluble (R,RP) diastereomer selectively crystallized in 64% yield in a typical second-order asymmetric transformation. Optically pure (S)-(-)-1, [α]D20 -210 (c 0.59, C6H6), was liberated from (R,RP)-5 with (R*,S*)-l,2-phenylenebis(methylphenylphosphine). The optically active phosphine in benzene racemizes over 6 h without significant redox disproportionation. The methoxyphosphine (±)-P(OMe)Ph(i-Pr), (±)-9, was also resolved by the method of metal complexation. Thus, fractional crystallization of (R,RP)- and (R,S P)-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C, N(methoxyphenyltsopropylphosphme)palladium(II), (R,RP)- and (R,SP)-8, followed by liberation of the respective optically active methoxyphosphines from the separated diastereomers with 1,2-bis(diphenylphosphino)ethane, gave (R)-(+)- and (S)-(-)-9 of 92% and 96% ee, respectively. The barrier to unimolecular inversion for (±)-9 was determined to be >82.9 ±0.5 kJ mol-1 by variable temperature 1H NMR spectroscopy. The substitution of fluoride in (R,RP)-5 by methoxide proceeds with predominant inversion of the configuration at phosphorus to give (R,RP)- and (R,SP)-8 with (R,SP)/(R,RP) = 1/5. The crystal structures of (R,RP)-5 and (R,RP)-8 have been determined: (R,RP)-5 (C23H28ClFNPPd) crystallizes in the orthorhombic space group F212121 with a = 9.967(2) Å, b= 10.998(4) Å, c = 21.324(3) Å, Z = 4, and R = 0.031; (R,RP)-8 (C24H31ClNOPPd) crystallizes in the space group P212121 with a = 10.444(3) Å, b = 12.146(3) Å, c = 19.047(2) Å, Z = 4, and R = 0.026. Show more